1. Field of the Invention
The present invention relates to a display device and a viewing angle control device. Particularly, the present invention relates to a display device and a viewing angle control device each of which makes it possible to switch to a mode in which an image to be seen is changed in accordance with a viewing direction.
2. Description of the Related Art
In recent years, electronic apparatuses have become lighter and lighter, so that an electronic apparatus, such as a portable phone or a mobile personal computer, which has a display can be taken out to and used in a public place. This has caused such a problem that a confidential document or information that a user wishes to individually browse is seen by a person near the user.
In response to this problem, there has been proposed a display device which can be set in a wide viewing angle display mode under normal conditions and which can be switched to a narrow viewing angle display mode when taken out to and used in a public place. The narrow viewing angle mode refers to a mode in which a user right in front of a display can see a normal display image and in which a plain image or another image is seen from an oblique direction. Further, by making it possible to switch to the wide viewing angle display mode, it is possible to deal with a situation where a wide viewing angle is required, e.g., where a shot image needs to be seen by a large number of people.
Examples of a part for carrying out such a display include a viewing angle variable element disclosed in Japanese Unexamined Patent Application No. 105958/1997 (Tokukaihei 9-105958; published on Apr. 22, 1997). According to the viewing angle variable element, a narrow viewing angle is obtained when liquid crystal molecules of a liquid-crystal layer provided between a pair of substrates are oriented in a direction perpendicular to the substrates, and a wide viewing angle is obtained when the liquid crystal molecules are oriented in a direction parallel to the substrates. Further, Japanese Unexamined Patent Application No. 62094/2004 (Tokukai 2004-62094; published on Feb. 26, 2004) describes viewing angle changing means for changing a viewing angle of information means by changing the orientation of liquid crystals provided between two glass plates.
Furthermore, there is a display device arranged so as to be divided into several zones, for, example, in which liquid crystals are oriented in different directions. With this arrangement, in cases where a display is seen from a direction other than the front direction in a narrow viewing angle mode, an image different from an image shown by the display can be seen. For example, Japanese Unexamined Patent Application No. 264768/2001 (Tokukai 2001-264768; published on Sep. 26, 2001) discloses a liquid crystal display device in which orienting films sandwiching liquid crystals therebetween are divided into a plurality of regions and in which the regions adjacent to one another have different directions of orientation. Further, Japanese Unexamined Patent Application No. 38035/2004 (Tokukai 2004-38035; published on Feb. 5, 2004) discloses a liquid crystal display device in which first and second liquid crystal cells having different viewing directions are alternately provided.
According to the arrangement of Tokukaihei 9-105958, the narrow viewing angle mode is set when the reflectance is changed by vertically orienting the liquid crystal molecules. However, such viewing angle control using the reflectance makes it difficult to retain image display quality.
Further, although Tokukai 2004-62094 teaches that the viewing angle of the display is controlled by changing the orientation of the liquid crystals, but fails to teach how to change the orientation of the liquid crystals. Therefore, viewing angle control cannot be realized.
Furthermore, the arrangement of Tokukai 2001-264768 teaches that a fixed pattern irrelevant to a display signal is seen from a direction other than the front direction. However, because of the structure, the pattern has its black and white reversed depending on whether it is seen from the right or left. Therefore, a display image cannot be appropriately hidden when the display image is seen from a direction other than the front direction. That is, when the pattern has a large non-transmission region in cases where the pattern is seen from the right, the pattern has a large transmission region in cases where the pattern is seen from the left. Therefore, the only way to hide the screen image when it is seen from both the right and left is to reduce the visibility of the screen image by covering the screen image with an image having transmission and non-transmission regions in a fifty-fifty proportion (e.g., an image patterned with hound's teeth checks). Further, such an image having transmission and non-transmission regions in a fifty-fifty proportion has too large a transmission region to hide the screen image, so that a sufficient visibility prevention effect cannot be obtained.
Further, according to the arrangement of Tokukai 2004-38035, a large number of small liquid crystal cells are arrayed on a substrate. However, such a liquid crystal display device has a complex arrangement, and therefore is difficult to manufacture.
As described above, there has been unknown a simply arranged display device, exhibiting high display quality, which makes it possible to switch to a mode in which a display image can be appropriately hidden when the display image is seen from an oblique direction.